public sealed class ImageWatermark : Watermark, 
	IDisposable

Public NotInheritable Class ImageWatermark
	Inherits Watermark
	Implements IDisposable

public ref class ImageWatermark sealed : public Watermark, 
	IDisposable

[<SealedAttribute>]
type ImageWatermark =  
    class
        inherit Watermark
        interface IDisposable
    end

foreach (string filePath in Directory.GetFiles(@"C:\Documents"))
{
    using (Watermarker watermarker = new Watermarker(filePath))
    {
        using (ImageWatermark watermark = new ImageWatermark(@"C:\watermark.png"))
        {
            watermark.HorizontalAlignment = HorizontalAlignment.Center;
            watermark.VerticalAlignment = VerticalAlignment.Center;
            watermarker.Add(watermark);
        }

        watermarker.Save();
    }
}